Electron discharge apparatus



April 13, 1943. MOTZ ELECTRON DISCHARGE APPARATUS Filed Dec. 11, 1940 R.WM H ATTRNEY Patented Apr. 13, 1943 ELEc'rRoN DISCHARGE APPARATUS HansMotz,

national Standard E York, N. Y.

Application December 11 In Great Brit (Cl. IZ50-27.5)

4 Claims.

This invention relates to electron discharge apparatus utilisingconcentrated electron beams and has application where it is desirablethat the beam current shall have a high intensity and density. It hasbeen found difficult to produce such beams because of the space chargeset up by the beam. The space charge tends to decelerate the beam, andin the eXtreme case stops the beam completely thus forming an unwantedvirtual cathode somewhere along the intended path of the beam.

In accordance with the present invention positive ions are utilised forthe purpose of neutralising the space charge, the ions being projectedin a beam along the electron path in the opposite direction to theelectrons.

In one aspect the invention resides in an electron discharge devicecomprising an electron source and a positive ion source, and means fordirecting electrons from the electron source towards the ion source andfor directing positive ions from the ion source towards the electronsource.

In another aspect an electron discharge device utilising a concentratedelectron beam is provided with an electron-emissive electrode adapted tofunction as a cathode and a positive-ion-emissive electrode adapted tofunction as an anode.

In a further aspect the invention resides in an electron dischargedevice comprising an electron gun and a positive-ion gun directed towardeach other.

As a source of positive ions I may employ a mass or layer cf barium,caesium or a compound thereof in or on a suitable carrier, a heaterresistance for said mass or layer and an ionising grid in front of saidmass or layer adapted to be maintained at a high temperature duringoperation of the device.

In particular, barium ions may be utilised because they have three otheruseful effects. Firstly any barium ions which may be neutralised andcondensed on any inner surface of the tube act as a getter. Secondly, ifa surface coated with a barium compound is used as an electron source,barium from the beam can be used to replenish the barium content of theelectron emitting surface. Thirdly, the barium ions also tend toneutralise the space charge near the electron emitting surface and thusmake it possible to use dispenser cathodes or electron emitting surfacesof complex shape, such as cathodes comprising vanes or tubes coated withemissive material and located Within an enclosing metal cylinder open atone end.

London, England, assignor to Inter- 'lectric Corporation, New

, 1940, Serial N0. 369,515

ain July 5, 1940l Caesium ions are also suitable for reasons similar tothe ones statedabove. Caesium ions have an advantage in that the caesiumafter use in the ionised state may be recovered by bringing differentparts of the tube ,to such temperatures that caesium is evaporatedfromthese surfaces which are kept warm, and condensed in a speciallyarranged cooled region.

The electron beam may be made to heat, the ion source; conversely theion beam may be used to heat the electron source; the amount of heatingcurrent for the ion or electron sources can then be reduced once thetube is running.

The ion beam may be produced by various methods. In one method thosesubstances are used which, when heated, generate a vapour which can beionised by the hot Wire method. In particular the vapour can be made topass a hot wire mesh and the ions formed can be focussed by the usualelectric and magnetic lenses.

An electron discharge device of the klystron oscillator type modified inaccordance with the invention is shown diagrammatically in the singlefigure of the accompanying drawing.

R and Rl are the toroidal resonators of the klystron with central gridsor apertures'G and back-coupling LI. 'I'he resonators are joined bydrift tube T. Electrons from a cathode K are concentrated in a beam byfocussing electrodes represented by FE. In passing through the resonatorRI (that is, across the iirst gap in the resonator system), they aremodulated in velocity. They subsequently become bunched in the drifttube T and are retarded in the second resonator R (that is, intraversing the second gap of the resonator system), thereby yieldingenergy to the resonator R. Part of the energy in resonator R is fed backover the coupling LI to excite resonator R l In applying the inventionto the above described structure, a positive-ion gun is provided at theend of the electron path for projecting positive ions towards thecathode.

In the structure shown, a barium compound such as barium berylliate orbarium metal B is provided in a container C surrounded by a resistanceheater H. A series of wires W forminga grid and adapted to reach a hightemperature during operation (either by bombardment or by means of anexternal current supply source) is arranged in front of the container Cfor ionising barium vapourised from the container, the grid electrode Wthus serving as an anode. The wires W, in the case of barium arecomposed of a material such as oXidised tungsten having a Work functionwhen hot, which is larger than the ionisation potential of the gas to beionsed. The barium ions in the structure shown are conc-entrated in abeam towards the cathode by means of a focussing electrode systemrepresented by FI.

The Whole structure shown may be enclosed in a vacuum-tight envelope Evvith suitable leading-in conductors sealed in it. Alternatively thevarious beam-forming electrodes may be disposed at the ends of a narrowglass or like tube projecting through the resonator system. In this casesimple apertures are provided in the resonators instead of grids.

Various modications Within the scope of the appended claims will bereadily appreciated.

What is claimed is:

1. Electron discharge device for operation at extremely high frequenciescomprising electron gun means, a rst resonator chamber, a secondresonator chamber, said chambers having apertures for permitting thepassage of the electron beam emitted by said gun means, collectorelectrode means disposed in the path of said beam, said collectorelectrode means comprising a source of positive ions, and means forfocusing positive andere ions from said collector electrode in a paththrough said resonator chambers.

2. An electron discharge device according to claim 1 in which saidsource of positive ions comprises a mass of alkaline earth metal, and aheater electrode for high temperature operation intermediate said massand said second resonator.

3. An electron discharge device according to claim 1 in which saidsource of positive ions comprises a mass of alkaline earth metal, aheater electrode for high temperature operation intermediate said massand said second resonator, and ion focusing electrode means intermediatesaid heater electrode and said second resonator.

4. An electron discharge device, including a cathode to serve as anelectron source, an anode to serve as a positive ion source, electrodemeans to focus electrons from said cathode on said anode, furtherelectrode means to focus positive ions from said anode on said cathode,said anode including a mass of an alkaline earth metal, a heater forsaid mass, and a heater grid for high temperature operation in front. ofsaid mass for ionizing vapor therefrom.

HANS MOTZ.

